This invention relates generally to medicines for the treatment of diseases and, more specifically to consistently stable formulations for polypeptide therapeutics.
With the advent of recombinant DNA technology, protein-based therapeutics have become continually and increasingly commonplace in the repertoire of drugs available to medical practitioners for the treatment of a wide range of diseases from cancer to autoimmune diseases. Along with the scientific and technical advances that have occurred in the production of recombinant proteins, another reason for the success of protein therapeutics is their high specificity towards targets and their ability to exhibit superior safety profiles when compared to small molecule therapeutics. The ability to employ biological molecules as pharmaceuticals in the treatment of diseases has significantly advanced medical care and quality of life over the past quarter of a century.
Proteins known to exhibit various pharmacological actions in vivo are now capable of being produced in large amounts for various pharmaceutical applications. Long-term stability of a therapeutic protein is a particularly beneficial criterion for safe, consistent and efficacious treatments. Loss of functionality of the therapeutic within a preparation will decrease its effective concentration for a given administration. Similarly, undesired modifications of a therapeutic can affect the activity and/or the safety of a preparation, leading to loss of efficacy and risk of adverse side effects.
Proteins are complex molecules with defined primary, secondary, tertiary and in some cases quaternary structures, all of which play a role in imparting specific biological function. Structural complexity of biological pharmaceuticals such as proteins make them susceptible to various processes that result in structural and functional instability as well as loss of safety. With respect to these instability processes or degradation pathways, a protein can undergo a variety of covalent and non-covalent reactions or modifications in solution. For example, protein degradation pathways can be generally classified into two main categories: (i) physical degradation or non-covalent pathways, and (ii) chemical or covalent degradation pathways.
Protein drugs are susceptible to the physical degradation process of irreversible aggregation. Protein aggregation is of particular interest in polypeptide production because it often results in diminished bioactivity that affects drug potency, and also can elicit serious immunological or antigenic reactions in patients. Chemical degradation of a protein therapeutic, including degradation of the chemical structure by, for example, chemical modification, also has been implicated in increasing its immunogenic potential. Thus, stable protein formulations require that both physical and chemical degradation pathways of the drug be minimized.
Proteins can degrade, for example, via physical processes such as interfacial adsorption and aggregation. Adsorption can significantly impact a protein drug's potency and stability. It can cause an appreciable loss in potency of low concentration dosage forms. A second consequence is that unfolding mediated adsorption at interfaces can often be an initiating step for irreversible aggregation in solution. In this respect, proteins tend to adsorb at liquid-solid, liquid-air, and liquid-liquid interfaces. Sufficient exposure of a protein's core at a hydrophobic surface can result in adsorption as a consequence of agitation, temperature or pH induced stresses. Further, proteins also are sensitive to, for example, pH, ionic strength, thermal stress, shear and interfacial stresses, all of which can lead to aggregation and result in instability. Another consequence of aggregation is particle formation an important consideration in liquid and lyophilized protein pharmaceuticals.
Proteins also are subject to a variety of chemical modification and/or degradation reactions such as deamidation, isomerization, hydrolysis, disulfide scrambling, beta-elimination, oxidation and adduct formation. The principal hydrolytic mechanisms of degradation include peptide bond hydrolysis, deamidation of asparagine and glutamine, isomerization of aspartic acid and cyclization of glutamic acid leading to pyro-glutamic acid. A common feature of the hydrolytic degradation pathways is that one significant formulation variable, with respect to the rates of the reactions, is the solution pH.
For example, the hydrolysis of peptide bonds can be acid or base catalyzed. Asparagine and glutamine deamidation also are acid catalyzed below a pH of about 4. Asparagine deamidation at neutral pH occurs through a succinimidyl intermediate that is base catalyzed. The isomerization and racemization of aspartic acid residues can be rapid in slightly acidic to neutral pH (pH 4-8). In addition to the generalized pH effects, buffer salts and other excipients can affect the rates of the hydrolytic reactions.
Other exemplary degradation pathways include beta-elimination reactions, which can occur under alkaline pH conditions and lead to racemization or loss of part of the side-chain for certain amino acids. Oxidations of methionine, cysteine, histidine, tyrosine and tryptophan residues are exemplary covalent degradation pathways for proteins.
Because of the number and diversity of different reactions that can result in protein instability the composition of components in a formulation can significantly affect the extent of protein degradation and, consequently, the safety and efficacy of the therapeutic. The formulation of a polypeptide also can affect the ease and frequency of administration and pain upon injection. For example, immunogenic reactions have not only been attributed to protein aggregates but also to mixed aggregates of the therapeutic protein with an inactive component contained in the formulation (Schellekens, H., Nat. Rev. Drug Discov. 1:457-62(2002); Hesmeling, et al., Pharm. Res. 22:1997-2006 (2005)).
However, despite the advances made in the utilization of proteins in therapeutic treatments and the knowledge of the instability process they can undergo, there is still a need to develop formulations with enhanced long-term stability characteristics. A formulation that retains long-term stability under a variety of conditions would provide an effective means of delivering an efficacious and safe amount of the polypeptide. Retention of long-term stability in a formulation also would lower the production and treatment costs. Numerous recombinant or natural proteins could benefit from such consistently stable formulations and thereby provide more effective clinical results.
Thus, there exists a need for formulations that retain long-term stability under a variety of different manufacturing and storage conditions. The present invention satisfies this need and provides related advantages as well.